This portrait is only made with "flat circles" on a black
background. Every circle has a single color, a single tone and a single
size. I placed each circle one by one. It's a time consuming method.
Please see some details, the work in progress and other portraits here
below. If you wish, you can also view this making of my portrait of
Elvis Presley (video) to understand how I'm exploiting this technique
with circles...